There's a solenoid (electromagnet) in the contactor that runs on 120v. When the switch is closed, it energizes the electromagnet and closes the contacts (get it, contactor) completing the circuit between both halves of the contactor. Turn the switch off and the electromagnet is de-energized and the spring in the contactor opens the contacts breaking the circuit between the two halves. Typically used to switch higher voltages and amperages. It's used as a safety measure since SSR's can fail and when they do they typically fail closed allowing amps to flow. The contactor is a definite purpose device and can disconnect power to the element/outlet while leaving everything else powered on.

There's a solenoid (electromagnet) in the contactor that runs on 120v. When the switch is closed, it energizes the electromagnet and closes the contacts (get it, contactor) completing the circuit between both halves of the contactor. Turn the switch off and the electromagnet is de-energized and the spring in the contactor opens the contacts breaking the circuit between the two halves. Typically used to switch higher voltages and amperages. It's used as a safety measure since SSR's can fail and when they do they typically fail closed allowing amps to flow. The contactor is a definite purpose device and can disconnect power to the element/outlet while leaving everything else powered on.

That makes sense...thanks for explaining. Still trying to wrap my head around the different components and how they work together. This is helpful.

Where did you end up getting your contactors? The ones from the electrical diagram in your original post say "240V - 30A, 120V coil". Saw that you're running this on 120V 20amps, which as I understand is standard residential power. That is the same as what I plan to do.

I found all the other components that I need on Aubers site, but I don't see contactors that match the description in the electrical diagram...closest I can find is this:

Where did you end up getting your contactors? The ones from the electrical diagram in your original post say "240V - 30A, 120V coil". Saw that you're running this on 120V 20amps, which as I understand is standard residential power. That is the same as what I plan to do.

I found all the other components that I need on Aubers site, but I don't see contactors that match the description in the electrical diagram...closest I can find is this:

Hopefully this isn't splitting hairs; I just don't want to mess around (at all) when it comes to electricity and wiring, ya know?

There is no problem using a contactor that is rated for more amps, just do not want to use one rated for less. I went with the 20amp ones because they were cheaper at the time. I got them from Amazon. Now the 30 amp ones are cheaper if you factor in that they ship free with Prime. Here they are: Amazon 30amp Contactors. If you don't have Prime, you could always get some other stuff for your build to get to the $25 mark, such as a terminal block etc.

What sized batches are you doing? I am looking to do 10 and 15 gallon batches and want to be able to quickly ramp mash temps.

I am doing 10 gallon batches. So far when I wanted to raise to mashout, I use propane and the rims. Works quickly, but I have not tried with electrical element alone since I have capability to use both.